Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$232.32	11.156%	$258.2376	$258.24	$258.25	$258.20
Purchase #2	$95.48	9.735%	$104.775	$104.78	$104.80	$104.80
Purchase #3	$99.42	4.684%	$104.0768	$104.08	$104.10	$104.10
Purchase #4	$208.54	5.742%	$220.5144	$220.51	$220.50	$220.50
Purchase #5	$134.37	3.813%	$139.4935	$139.49	$139.50	$139.50
Purchase #6	$47.91	13.770%	$54.5072	$54.51	$54.50	$54.50
Purchase #7	$30.35	8.269%	$32.8596	$32.86	$32.85	$32.90
7 purchase totals =	$848.39		$914.4641	$914.47	$914.50	$914.50